Measurement and Correlation of Solubility of L–Tryptophan in Aqueous Solutions with a Wide Range of pH and Different Monovalent Counterions from 283.15 to 323.15 K,Journal of Solution Chemistry

The aqueous solubility of L-tryptophan was measured with a wide range of pH (1.00–12.50) and different monovalent counterions (Na+, K+, Cl− and \({\text{NO}}_{\text{3}}^{-}\)) from 283.15 to 323.15 K by using a static equilibrium method. The results showed that the solubility of L-tryptophan increased with increasing temperature and the solubility–pH profile was a “U” shape with the lowest value at the isoelectric point. Additionally, the distribution of the ionic forms of L-tryptophan as a function of pH was obtained using the knowledge of the acid–base equilibria of amino acids, and it was found that the isoelectric points increased with temperature. Moreover, different counterions were introduced by using different acids or bases during pH adjustment and their effect on the solubility of L-tryptophan was investigated, which showed that more L-tryptophan could be dissolved in the presence of K+ (or \({\text{NO}}_{\text{3}}^{-}\)) than Na+ (or Cl−). Besides, the modified Apelblat model and the NRTL model were successfully used to correlate the aqueous solubility data with all the average relative deviation less than 2.1%.

中文翻译：

L-色氨酸的水溶性在宽范围的 pH 值 (1.00–12.50) 和不同的单价抗衡离子 (Na + , K + , Cl −和\({\text{NO}}_{\text{3} }^{-}\)) 从 283.15 到 323.15 K 通过使用静态平衡方法。结果表明，L-色氨酸的溶解度随温度升高而增加，溶解度-pH曲线呈“U”形，等电点处的值最低。此外，利用氨基酸酸碱平衡的知识，获得了 L-色氨酸的离子形式随 pH 的分布，发现等电点随温度升高。此外，在pH调节过程中，通过使用不同的酸或碱引入不同的抗衡离子，并研究了它们对L-色氨酸溶解度的影响，这表明在K + (或\({\ text{NO}}_{\text{3}}^{-}\) ) 比 Na +（或Cl -）。此外，改进的Apelblat模型和NRTL模型被成功地用于关联水溶解度数据，所有平均相对偏差小于2.1%。